The present invention relates to fuel system valves, and particularly to a flow control valve for regulating the discharge of pressurized fuel vapor from a fuel tank. The present invention also relates to such valves which are tank-mounted for venting fuel vapor from various regions inside a vehicle fuel tank to a vapor-recovery canister or other destination. The present invention also relates to a tank valve which prevents liquid fuel within a tank venting system from entering and contaminating a vapor-recovery canister within the system.
Is it well understood that significant quantities of fuel vapor can escape from a fuel tank through the filler neck to the atmosphere during the refueling of motor vehicles. Early attempts to control the vapor escape focused upon control devices fitted to a fuel-dispensing pump nozzle connected to a service station fuel pump. Later, control devices mounted directly on-board the vehicle were developed. See, for example, U.S. Pat. No. 4,816,045 to Szlaga et al., relating to a vapor-recovery system mounted on the fuel tank filler neck. Tank venting systems which mount to a fuel tank have also been developed as shown, for example, in U.S. Pat. No. 5,156,178 to Harris.
In additional to controlling vapor escape, well-designed tank venting systems also assist in controlling the amount of liquid fuel which can be pumped into the fuel tank during refueling. For safety reasons, fuel systems are designed so that the fuel tank is never completely filled with liquid fuel. Rather, at least a predetermined portion of the space inside the fuel tank is left for liquid fuel and fuel vapor expansion. Although fuel pump nozzles typically include sensors for shutting off the flow of liquid fuel into the fuel tank when the fuel tank is nearly filled, fuel pump users may manually override the sensors by continuing to pump fuel after the sensors have automatically and temporarily shut the pump nozzle off. To assist in preventing tank overfill under such conditions, a tank venting system is usually provided with a xe2x80x9cfill-limitxe2x80x9d control system which assists in triggering the nozzle shut-off mechanism when the level of liquid fuel in the fuel tank has risen to a predetermined level. See, for example, the fill-limit control system disclosed in U.S. Pat. No. 4,816,045 to Szlaga et al.
It has also long been recognized that fuel vapor is generated in the fuel tank during operation of the vehicle, for example, by evaporation or by sloshing of the liquid fuel against the walls of the tank. Excessive pressure can build up in the fuel tank as a result of the newly formed fuel vapor unless control devices are provided to vent the fuel vapor from the fuel tank during vehicle operation. Such valves have been referred to as xe2x80x9crun-lossxe2x80x9d valves or tank venting rollover valves because they handle the fuel vapor loss during vehicle run and are capable of preventing liquid fuel carryover during vehicle rollover.
Vehicle fuel systems are known to include pressure-relief valves mountable on either fuel tanks or filler necks. In general, the venting portion of these conventional valve assemblies has included a pressure-relief valve positioned in a vent passageway having a surface exposed to the pressure in the tank and a yieldable control spring urging the pressure-relief valve normally to close the vent passageway. In response to a predetermined superatmospheric pressure, the pressure-relief valve is urged in opposition to the control spring to open the vent passageway.
Examples of valves and systems as discussed above include U.S. Pat. Nos. 5,687,778 to Harris; 5,666,989 to Roetker; 4,760,858 to Szlaga and 4,742,844 to Szlaga.
Features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.